i) Field of the Invention
The present invention relates to a cathode-ray tube having a reduction device of an alternating electric field emitted by a deflection yoke.
ii) Description of the Related Arts
In FIG. 1, there is shown a conventional cathode-ray tube. In this cathode-ray tube, a funnel part 1 is composed of a neck part 1a, a cone part 1b and a funnel body part 1c having a high voltage anode button 1d and is secured to a panel part 2 by using a frit seal. A neck seal line 1e is a coupling part for connecting the neck part 1a and the cone part 1b and is formed of glass somewhat thin in thickness, and thus is a weak part compared with other parts. As described above, the funnel part 1 and the panel part 2 constitute a glass bulb 20. An electron gun 3 is mounted and sealed within the neck part 1a. An implosion-protection band 4 for ensuring an implosion-proof property is wound around the side surfaces of the panel part 2, and four latch members 4a, for suspending the glass bulb 20 within a box frame (not shown), are integrally formed at the four corner portions of the band 4. A silicon resin film 5 for insulation is formed around the high voltage anode button 1d provided on the funnel body part 1c, and a conductive film 6 for adding a capacitance to the cathode-ray tube is formed on an external surface of the funnel body part 1c. This conductive film 6 is usually formed by applying graphite. A numeral 28 denotes a tube axial of a straight line parallel with the neck part 1a.
As shown in FIG. 2, a deflection yoke 7 for deflecting the electron beam is mounted on the above-described cathode-ray tube between the cone part 1b and the neck part 1a. As shown in FIG. 3, the deflection yoke 7 is composed of a horizontal deflection coil 7a, a vertical deflection coil 7b and a deflection yoke body part 7c.
The operation of the above-described cathode-ray tube will be described. That is, when the electron beam is irradiated by the electron gun 3 sealed within the neck part 1a, and the irradiated electron beam is deflected a predetermined amount in the horizontal and vertical directions by the horizontal deflection coil 7a and the vertical deflection coil 7b of the deflection yoke 7 to scan on a fluorescent film formed on the internal surface of the panel part 2. As a result, a desired image is projected on the panel part 2. At this time, the deflection width is in inverse proportion to a square root of a voltage applied to the high voltage anode button 1d.
In the conventional cathode-ray tube described above, no measures for shielding an alternating electric field radially generated around the deflection yoke during the deflection of the electron beam by the deflection yoke are provided. Thus the alternating electric field harmful to the human body permeates the funnel part 1 and the panel part 2 of the cathode-ray tube to irradiate forwards from the cathode-ray tube.
For reducing an influence on a radiation line of the electron beam due to a leakage magnetic field from a flyback transformer and the like, for example, as disclosed in Japanese Patent Laid-Open No. Sho 61-138433, a covering member for annularly covering a focusing electrode system constituting an electron gun by using a non-magnetic conductive magnetic shield body has been proposed. However, this covering member does not pay any consideration to the alternating electric field and can not reduce the alternating electric field as before.